Cathode ray tube

ABSTRACT

A cathode ray tube includes a panel having a substantially flat outer surface and an inner curved surface with a phosphor screen. The panel has a substantially rectangular effective screen portion with two long sides parallel to each other, two short sides parallel to each other and four rounded edges interconnecting each long side and the neighboring short side. The effective screen portion is structure such that a first line V1 interconnecting centers of the long sides, a second line H1 interconnecting centers of the short sides and a third line D1 interconnecting centers of the rounded edges opposite to each other meet at a point. The effective screen portion has a first thickness Tv at the centers of the long sides, a second thickness Th at the centers of the short sides, a third thickness Td at the centers of the edges and a fourth thickness Tc at the meeting point of the all three lines V1, H1 and D1. A shadow mask is disposed within the panel so that the shadow mask faces the inner curved surface of the panel. The shadow mask has a curvature corresponding to the inner curved surface of the panel. The ratio of the second thickness Th to the third thickness Td while subtracting the fourth thickness Tc from each thickness satisfies the following condition: 0.75(Th−Tc)/Td−Tc)≦0.85, and the ratio of the first thickness Tv to the thickness Td while subtracting the fourth thickness Tc from each thickness satisfies the following condition: 0.75≦(Tv−Tc)/(Td−Tc)≦0.85.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a reissue of U.S. Pat. No. 6,407,496 B2 which claimspriority of continuation of application Ser. No. 09/440,216, filed Nov.15, 1999is now , which issued as U.S. Pat. No. 6,232,712, the disclosureof which is incorporated fully herein by reference, which in turn claimspriority of Korean application No. 98-48556, filed Nov. 13, 1998.

FIELD OF THE INVENTION

The present invention relates to a cathode ray tube (CRT) and, moreparticularly, to a CRT that can minimize raster distortion of electronbeams while maintaining the structural strength of a shadow mask.

BACKGROUND OF THE INVENTION

Generally, a faceplate panel for CRTs has a convex-shaped lens withcurved inner and outer surfaces. The convex lens-shaped panel isadvantageous in various aspects such as convenience in formation,stability in strength and adaptability for shadow mask application.

However, to the eye of the viewer, it is desirable that the screen imagebe displayed substantially flat. For this purpose, several attempts havebeen made to form the inner and outer surfaces of the faceplate panelwith a flat shape while maintaining normal display characteristics ofthe CRT. It is found that when a flat panel is employed for the displayscreen problems occur in both the convergence characteristics ofelectron beams and in the strength of a shadow mask. For instance,because the flat-shaped inner surface of the panel is naturally formedwith a flat phosphor screen, it becomes difficult to deflect threeelectron beams of red R, green G and blue B on correct phosphors on thephosphor screen. Furthermore, because the shadow mask facing theflat-shaped inner surface of the panel should also be flat, a desirableshadow mask strength cannot be achieved using the common shadow maskforming technique.

In addition, there is a problem with the flat-panel CRT from thestandpoint of the viewer. When the viewer watches a monitor with aflat-shaped panel, the viewer feels that the screen image is sunken atits center portion while protruded at its peripheral portion.

Therefore, it is preferably that the outer surface of the panel is flatwhereas the inner surface of the panel is curved.

In such a faceplate panel, as the overall curvature radius of the innercurved surface of the panel becomes smaller, the panel is more easilyproduced and the shadow mask has a more stable structure capable ofreducing a doming phenomenon. However, when the curvature radius fallsshort of a minimum effective value, the peripheral portion of the panelbears an undesirably large thickness and this results in poor productionefficiency as well as high production cost. Furthermore, thetransmission rate of the peripheral portion becomes poor due to itslarge thickness, causing brightness failure.

In order to overcome such problems, various techniques are proposed fora one-sided flat panel CRT application. For example, some techniques aredisclosed in Japanese Patent Laid Open Publication No. 6-36710 and No.6-644926. However, the technical details are not specified forpreserving the structural strength of the shadow mask which should bere-designed pursuant to the curvature radii varying at differentpositions of the inner curved surface of the panel.

Furthermore, the prior art does not discriminate the desired thicknessratios of a diagonal portion of the panel to the peripheral portion forminimizing distortion of the screen image. Therefore, when the CRT panelis manufactured on the basis of the above-identified techniques, theaforementioned problems remain unsolved.

In the usual sized flat-panel 21-inch, 25-inch and 29-inch CRTs, thethickness ratios of the peripheral portion of the panel to the centerportion are 3.13, 2.91 and 2.72, respectively. These ratios are so highthat they result in poor production efficiency as well as brightnessfailure.

SUMMARY OF THE INVENTION

It is an object of an embodiment of the present invention to provide aCRT that can minimize raster distortion of electron beams whilemaintaining structural strength of a shadow mask.

This and other objects may be achieved by a CRT including a panel havinga substantially flat outer surface and an inner curved surface with aphosphor screen. The panel has a substantially rectangular effectivescreen portion with two long sides parallel to each other, two shortsides parallel to each other and four rounded edges interconnecting eachlong side and the neighboring short side. The effective screen portionstructured such that a first line V1 interconnecting centers of the longsides, a second line H1 interconnecting centers of the short sides and athird line D1 interconnecting centers of the rounded edges opposite toeach other meet at a point. The effective screen portion has a firstthickness Tv at the centers of the long sides, a second thickness Th atthe centers of the short sides, a third thickness Td at the centers ofthe edges and a fourth thickness Tc at the meeting point of the threelines V1, H1 and D1. A shadow mask is disposed within the panel so thatit faces the inner curved surface of the panel. The shadow mask has acurvature corresponding to the inner curved surface of the panel.

The ratio of the second thickness Th to the third thickness Td whilesubtracting the fourth thickness Tc from each thickness satisfies thefollowing condition: 0.75≦(Th−Tc)/(Td−Tc)≦0.85, and the ratio of thefirst thickness Tv to the third thickness Td while subtracting thefourth thickness Tc from each thickness satisfies the followingcondition: 0.75≦(Tv−Tc)/(Td−Tc)≦0.85. The ratio of the third thicknessTd to the fourth thickness Tc satisfies the following condition:Td/Tc≦2.

The effective screen portion of the panel has a first curvature radiusRv on the first line V1, a second curvature radius Rh on the second lineH1 and a third curvature radius Rd on the third line D1. The curvatureradii Rv, Rh and Rd have an inter-relation of Rv≦Rd≦Rh.

DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a partial sectional perspective view of a CRT with a panelaccording to a preferred embodiment of the present invention;

FIG. 2 is a front view of an effective screen portion of the panel shownin FIG. 1;

FIG. 3 is a sectional view of the panel shown in FIG. 1 taken along thevirtual line V1 of FIG. 2;

FIG. 4 is another sectional view of the panel shown in FIG. 1 takenalong the virtual line H1 of FIG. 2; and

FIG. 5 is another sectional view of the panel shown in FIG. 1 takenalong the virtual line D1 of FIG. 2.

DETAILED DESCRIPTION

As shown in FIG. 1, a CRT according to a preferred embodiment of thepresent invention includes a neck 4 having an electron gun 2 therein, afunnel 6 connected to the neck 4, and a panel 8 sealed to the funnel 6.

The panel 8 has an inner curved surface with a phosphor screen (notshown) and a substantially flat outer surface. A shadow mask 10 isdisposed within the panel 8 and faces the inner curved surface of thepanel 8. The shadow mask 10 is curved so that it can be adapted to theinner curved surface of the panel 8.

As shown in FIG. 2, the effective screen portion of the panel 8 has twolong sides 12 parallel to each other, two short sides 14 parallel toeach other, and four rounded edges 16 interconnecting each long side 12and the neighboring short side 14. As shown in the drawing, a firstvirtual line V1 may be drawn such that it interconnects centers of thelong sides 12. A second virtual line H1 may be drawn such that itinterconnects centers of the short sides 14. A third virtual line D1 maybe drawn such that it interconnects centers of the edges 16 opposite toeach other. The three virtual lines V1, H1 and D1 are indicated by longand short dashed lines in the drawing, and meet at a point 18.

The effective screen portion of the panel 8 has a first thickness Tv atthe centers of the long sides 12, a second thickness Th at the centersof the short sides 14, a third thickness Td at the centers of the edges16, and a fourth thickness Tc at the meeting point 18 of the threevirtual lines V1, H1 and D1.

The ratio of the second thickness Th to the third thickness Td whilesubtracting the fourth thickness Tc from each thickness is establishedto satisfy the following condition: 0.75≦(Th−Tc)/(Td−Tc)≦0.85.Furthermore, the ratio of the first thickness Tv to the third thicknessTd while subtracting the fourth thickness Tc from each thickness isestablished to satisfy the following condition:0.75≦(Tv−Tc)/(Td−Tc)≦0.85.

In the above conditions, when the minimum value is smaller than 0.75,raster distortion due to the deflection of the electron beams increases.In contrast, when the maximum value is higher than 0.85, the innersurface of the panel 8 has an excessively small curvature, and theshadow mask 10 accordingly has an overall curvature so small that itcannot adequately maintain its strength.

As shown in FIG. 3, the first thickness Tv is a value measured at thethickest portion of the effective screen area on the first virtual lineV1. As shown in FIG. 4, the second thickness Th is a value measured atthe thickest portion of the effective screen area on the second virtualline H1. As shown in FIG. 5, the third thickness Td is a value measuredat the thickest portion of the effective screen area on the thirdvirtual line D1.

The values satisfying the above-identified thickness conditions in a25-inch CRT panel and a 29-inch CRT panel are indicated in Table 1.

TABLE 1 25-inch CRT panel 29-inch CRT panel Td-Tc (mm) 25.4 26.3 Th-Tc(mm) 20.0 21.8 Tv-Tc (mm) 20.8 20.3 (Th-Tc)/(Td-Tc) 0.79 0.83(Tv-Tc)/(Td-Tc) 0.82 0.77

Meanwhile, the ratio of the third thickness Td to the fourth thicknessTc is established to satisfy the condition of Td/Tc≦2. In thiscondition, the screen image distortion can be effectively minimized.

The inner curved surface of the panel 8 has a first curvature radius Rvon the virtual line V1, a second curvature radius Rh on the secondvirtual line H1, and a third curvature radius Rd on the third virtualline D1. These curvature radii Rh, Rv and Rd have an inter-relation ofRV≦Rd≦Rh.

In a preferred embodiment of the present invention, the ratio of thethickness Th to the thickness Tc is established to satisfy the followingcondition: 1.4≦Th/Tc≦1.6. Furthermore, the ratio of the third thicknessTd to the fourth thickness Tc is established to satisfy the followingcondition: 1.7≦Td/Tc ≦2.0. In additional embodiments, the inner curvedsurface of the panel 8 may have a unique curvature radius or varyingcurvature radii at different positions. Under these conditions, thepanel 8 also exhibits good performance characteristics.

As described above, the inventive CRT has a panel with an effectivescreen portion that is structured to bear ideal thickness ratios amongits respective portions as well as suitable curvature radii. As aresult, raster distortion of the electron beams is minimized andsuitable structural strength of the corresponding shadow mask isobtained.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A cathode ray tube comprising: a panel having a substantially flatouter surface and an inner curved surface with a phosphor screen, thepanel having a substantially rectangular effective screen portion withtwo long sides parallel to each other, two short sides parallel to eachother and four rounded edges each interconnecting each a long side andthe a neighboring short side respectively, the effective screen portionbeing structured such that a first line V1 interconnecting centers ofthe long sides, a second line H1 interconnecting centers of the shortsides and a third line D1 interconnecting centers of the rounded edgesopposite to each other meet at a point, the effective screen portionhaving a first thickness Tv at the centers of the long sides, a secondthickness Th at the centers of the short sides, a third thickness Td atthe centers of the edges and a fourth thickness Tc at the meeting pointof the first to third lines V1, H1 and D1; wherein the ratio of thesecond thickness Th to the third thickness Td while subtracting thefourth thickness Tc from each thickness satisfies the followingcondition: 0.75≦(Th−Tc)/(Td−Tc)≦0.85, and the ratio of the firstthickness Tv to the third thickness Td while subtracting the fourththickness Tc from each thickness satisfies the following condition:0.75≦(Tv−Tc)/(Td−Tc)≦0.85.
 2. The cathode ray tube of claim 1 whereinthe ratio of the third thickness Td to the fourth thickness Td satisfiesthe following condition: Td/Tc≦2.
 3. The cathode ray tube of claim 1wherein the effective screen portion of the panel has a first curvatureradius Rv at the first line V1, curvature radius Rh at the second lineH1 and a third curvature radius Rd at the third line D1, and thecurvature radii Rv, Rh and Rd have an inter-relation of Rv≦Rd≦Rh.
 4. Acathode ray tube comprising: a panel having a substantially flat outersurface and an inner curved surface with a phosphor screen, the panelhaving a substantially rectangular effective screen portion with twolong sides parallel to each other, two short sides parallel to eachother and four rounded edges each interconnecting each a long side andthe a neighboring short side respectively, the effective screen portionbeing structured such that a first line V1 interconnecting centers ofthe long sides, a second line H1 interconnecting centers of the shortsides and a third line D1 interconnecting centers of the rounded edgesopposite to each other meet at a point, the effective screen portionhaving a first thickness Tv at the centers of the long sides, a secondthickness Th at the centers of the short sides, a third thickness Td atthe centers of the edges and a fourth thickness Tc at the meeting pointof the first to third lines V1, H1 and D1; wherein the ratio of thesecond thickness Th to the fourth thickness Tc satisfies the followingcondition: 1.4≦Th/Tc≦1.6, and the ratio of the third thickness Td to thefourth thickness Tc satisfies the following condition: 1.7≦Td/Tc≦2.0. 5.The cathode ray tube of claim 4 wherein the effective screen portion ofthe panel has a first curvature radius Rv on the first line V1, a secondcurvature radius Rh on the second line H1 and a third curvature radiusRd on the third line D1, and the curvature radii Rv, Rh and Rd have aninter-relation of Rv≦Rd≦Rh.
 6. The cathode ray tube of claim 5 whereinthe inner curved surface of the panel has a unique curvature radius orvarying curvature radii at different positions.
 7. The cathode ray tubeof claim 6 wherein the curvature radii Rv, Rh, and Rd are all eitherconstant throughout the inner surface of the panel or varying atdifferent positions.
 8. A cathode ray tube comprising: a panel having asubstantially flat outer surface and an inner curved surface with aphosphor screen, the panel having a substantially rectangular effectivescreen portion with two first sides parallel to each other, two secondsides parallel to each other, the second two sides being shorter thanthe first two sides, and four rounded edges each interconnecting one ofthe first sides with one of the second sides, the effective screenportion having a first thickness Tv at a center of one of the firstsides, a second thickness Th at a center of one of the second sides, athird thickness Td at a center of one or the rounded edges and a fourththickness Tc at a center of the effective screen portion; and wherein athickness ratio of the effective screen portion satisfies the followingconditions: 0.75≦(Th−Tc)/(Td−Tc)≦0.85, and 0.75≦(Tv−Tc)/(Td−Tc)≦0.85. 9.The cathode ray tube of claim 8 wherein the thickness ratio of theeffective screen portion further satisfies the following condition:Td/Tc≦2.
 10. The cathode ray tube of claim 8 wherein the effectivescreen portion of the panel has a curvature radius along a first linebetween the centers of the first sides, a curvature radius along asecond line between the centers of the second sides, and a curvatureradius along a diagonal line between the centers of two of the roundedcorners edges, wherein the maximum curvature of radius along the firstline and the minimum curvature of radius along the second line are equalto the curvature of radius along the diagonal line.
 11. A cathode raytube comprising: a panel having a substantially flat outer surface andan inner curved surface with a phosphor screen, the panel having asubstantially rectangular effective screen portion with two first sidesparallel to each other, two second sides parallel to each other, thesecond two sides being shorter than the first two sides, and fourrounded edges each interconnecting one of the first sides with one ofthe second sides, the effective screen portion having a first thicknessTv at a center of one of the first sides, a second thickness Th at acenter of one of the second sides, a third thickness Td at a center ofone of the edges and a fourth thickness Tc at a center of the effectivescreen portion; and wherein a thickness ratio of the effective screenportion satisfies the following conditions: 1.4≦Th/Tc≦1.6, and1.7≦Td/Tc≦2.0.
 12. The cathode ray tube of claim 11 wherein theeffective screen portion of the panel has a curvature radius along afirst line between the centers of the first sides, a curvature radiusalong a second line between the centers of the second sides, and acurvature radius along a diagonal line between the centers of two of therounded corners edges, wherein the maximum curvature of radius along thefirst line and the minimum curvature of radius along the second line areequal to the curvature of radius along the diagonal line.
 13. A cathoderay tube comprising: a panel having a substantially flat outer surfaceand an inner curved surface with a phosphor screen, the panel having aneffective screen portion with two first sides substantially parallel toeach other, two second sides substantially parallel to each other andedges, the edges located where each said first side and each neighboringsaid second side meet, the effective screen portion being structuredsuch that a first line V1 interconnecting centers of the first sides, asecond line H1 interconnecting centers of the second sides and a thirdline D1 interconnecting the edges which are opposite to each other, meetat a point, the effective screen portion having a first thickness Tv atthe centers of the first sides, a second thickness Th at the centers ofthe second sides, a third thickness Td at the centers of the edges and afourth thickness Tc at the meeting point of the first, second and thirdlines V1, H1 and D1; wherein the ratio of the second thickness Th to thethird thickness Td while subtracting the fourth thickness Tc from eachthickness satisfies the following condition: 0.75≦(Th−Tc)/(Td−Tc)≦0.85,and the ratio of the first thickness Tv to the third thickness Td whilesubtracting the fourth thickness Tc from each thickness satisfies thefollowing condition: 0.75≦(Tv−Tc)/(Td−Tc)≦0.85.
 14. The cathode ray tubeof claim 13 wherein the ratio of the third thickness Td to the fourththickness Td satisfies the following condition: Td/Tc≦2.
 15. The cathoderay tube of claim 13 wherein the effective screen portion of the panelhas a first curvature radius Rv at the first line V1, curvature radiusRh at the second line H1 and a third curvature radius Rd at the thirdline D1, and the curvature radii Rv, Rh and Rd have an inter-relation ofRv≦Rd≦Rh.
 16. A cathode ray tube comprising: a panel having asubstantially flat outer surface and an inner curved surface with aphosphor screen, the panel having an effective screen portion with twofirst sides substantially parallel to each other, two second sidessubstantially parallel to each other and edges, the edges located whereeach said first side and each neighboring said second side meet, theeffective screen portion being structured such that a first line V1interconnecting centers of the first sides, a second line H1interconnecting centers of the second sides and a third line D1interconnecting the edges which are opposite to each other, meet at apoint, the effective screen portion having a first thickness Tv at thecenters of the long sides, a second thickness Th at the centers of theshort sides, a third thickness Td at the centers of the edges and afourth thickness Tc at the meeting point of the first, second and thirdlines V1, H1 and D1; wherein the ratio of the second thickness Th to thefourth thickness Tc satisfies the following condition: 1.4≦Th/Tc≦1.6,and the ratio of the third thickness Td to the fourth thickness Tcsatisfies the following condition: 1.7≦Td/Tc≦2.0.
 17. The cathode raytube of claim 16 wherein the effective screen portion of the panel has afirst curvature radius Rv on the first line V1, a second curvatureradius Rh on the second line H1 and a third curvature radius Rd on thethird line D1, and the curvature radii Rv, Rh and Rd have aninter-relation of Rv≦Rd≦Rh.
 18. The cathode ray tube of claim 17 whereinthe inner curved surface of the panel has a unique curvature radius orvarying curvature radii at different positions.
 19. The cathode ray tubeof claim 18 wherein the curvature radii Rv, Rh, and Rd are all eitherconstant throughout the inner surface of the panel or varying atdifferent positions.
 20. A cathode ray tube comprising: a panel having asubstantially flat outer surface and an inner curved surface with aphosphor screen, the panel having an effective screen portion with twofirst sides substantially parallel to each other, two second sidessubstantially parallel to each other, and edges, the edges located whereeach said first side and each neighboring said second side meet, theeffective screen portion having a first thickness Tv at a center of oneof the first sides, a second thickness Th at a center of one of thesecond sides, a third thickness Td at one of the edges and a fourththickness Tc at a center of the effective screen portion; and wherein athickness ratio of the effective screen portion satisfies the followingconditions: 0.75≦(Th−Tc)/(Td−Tc)≦0.85, and 0.75≦(Tv−Tc)/(Td−Tc)≦0.85.21. The cathode ray tube of claim 20 wherein the thickness ratio of theeffective screen portion further satisfies the following condition:Td/Tc≦2.
 22. The cathode ray tube of claim 20 wherein the effectivescreen portion of the panel has a curvature radius along a first linebetween the centers of the first sides, a curvature radius along asecond line between the centers of the second sides, and a curvatureradius along a diagonal line between two of the edges, wherein themaximum curvature of radius along the first line and the minimumcurvature of radius along the second line are equal to the curvature ofradius along the diagonal line.
 23. A cathode ray tube comprising: apanel having a substantially flat outer surface and an inner curvedsurface with a phosphor screen, the panel having an effective screenportion with two first sides substantially parallel to each other, twosecond sides substantially parallel to each other, and edges, the edgeslocated where each said first side and each neighboring said second sidemeet, the effective screen portion having a first thickness Tv at acenter of one of the first sides, a second thickness Th at a center ofone of the second sides, a third thickness Td at a center of one of theedges and a fourth thickness Tc at a center of the effective screenportion; and wherein a thickness ratio of the effective screen portionsatisfies the following conditions: 1.4≦Th/Tc≦1.6, and 1.7≦Td/Tc≦2.0.24. The cathode ray tube of claim 23 wherein the effective screenportion of the panel has a curvature radius along a first line betweenthe centers of the first sides, a curvature radius along a second linebetween the centers of the second sides, and a curvature radius along adiagonal line between two of the edges, wherein the maximum curvature ofradius along the first line and the minimum curvature of radius alongthe second line are equal to the curvature of radius along the diagonalline.